1. Field of the Invention
The present invention relates to a method and apparatus of processing audio data having a system header and, more particularly, to a method and apparatus of recording a system header of audio data formed by a program stream based on the MPEG (Moving Picture Experts Group) standard.
2. Description of the Related Art
A prior art disclosing an AV (Audio Visual) data recording/playback system for mainly recording video data is described in, e.g., Japanese Patent No. 3026808. The prior art aims to facilitate recording and editing and realize on-memory time search by using a memory LSI (Large Scale Integrated circuit) of about 512 KB. AV data processed in this system is based on a program stream of the MPEG standard. The AV data includes one or more GOPs (Group Of Pictures), and is configured as a GOP set (VOB: Video OBject) having a VOBU (Video OBject Unit) structure whose playback time is 0.4 to 1.0 sec. Manager data for managing the AV data has time search information. The time search information has a hierarchical structure in which time entry information indicating time entry for, e.g., every 10 sec is added to VOBU entry information for managing each VOBU information as an entry table.
In the above prior art, recording of video data is essential, so the recording time for a DVD (Digital Versatile Disk) disk capacity of 4.7 GB is about 8 hrs. Therefore, even a time map structure for all entries of VOBU information (3 bytes: size and access information) whose playback time unit is about 0.5 sec occupies a capacity of at most about 200 KB. This is not a serious problem compared to the whole manager data processed in on-memory processing. Also, in the above prior art, by inserting a system header for each VOBU which forms a VOB, editing based on an MPEG program stream can be processed for each VOBU.
On the other hand, an audio data recording/playback system (e.g., a system of the DVD audio recording standard) for mainly recording audio data can record only sound. For example, when a 96-Kbps compressed audio code is used, the recording time for a DVD disk capacity of 4.7 GB reaches about 100 hrs. In this case, 1,000 pieces or more of music can be recorded and played back even when the playing time of one piece of music is about 5 min. Therefore, the manager data (e.g., the time entry information) must handle data of 1,000 pieces or more of music.
If a unit structure (AOBU: Audio OBject Unit) similar to the VOBU in the above-mentioned prior art is used and a set (AOB) of this AOBU structure whose unit is 1 sec is formed for audio data of 1,000 pieces or more of music, the size of a table of AOBU entry information (2 bytes: size and access information) exceeds 700 KB. Consequently, this information alone increases the load on the on-memory processing and makes other important manager data difficult to process.
That is, the conventional video recording system constructs a video data unit structure having a system header at its start on a large-capacity disk. The system poses no problem because editing is performed for each unit. However, an audio recording system capable of recording audio data on a large-capacity disk by using various compression systems can record and play back 1,000 pieces of music for about 100 hrs. Accordingly, in the hierarchical structure of an audio data unit structure, the size manager data comprising a time map and the like becomes enormous and exceeds the range capable of being processed by on-memory processing if the memory size is at most about 512 KB.
On the other hand, if a unit structure is disused to reduce this enormous manager data and make rapid on-memory processing feasible, a system header disappears by deletion, editing, or the like.